Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N2/00—Magnetotherapy
  • A61N2/02—Magnetotherapy using magnetic fields produced by coils, including single turn loops or electromagnets
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N2/00—Magnetotherapy
  • A61N2/004—Magnetotherapy specially adapted for a specific therapy
  • A61N2/006—Magnetotherapy specially adapted for a specific therapy for magnetic stimulation of nerve tissue

Definitions

• the present invention relates to a method according to the preamble of claim 1 and an apparatus according to the preamble of claim 9.
• Methods and apparatuses of the kind discussed herein are used for measuring and examining the response of biological tissue through stimulating the same by electromagnetic means.
• Magnetic stimulators deliver the changing magnetic field by means of a coil.
• the coil transduces the electric energy fed by the power source of the stimulator into magnetic field energy.
• the coil can be an integral or separate part of a magnetic stimulator.
• Magnetic stimulation has been found a risk- and pain-free method of stimulating human brain, peripheral nervous system or muscles.
• the method has a plurality of applications in basic research, diagnosis and therapy.
• Magnetic stimulation of the brain also involves activation of skin on the skull.
• the electromagnetic field induced by the coil is weaker the greater the distance from the coil.
• the field strength on the scalp is manyfold.
• This high-level excitation causes contraction of scalp muscles and activa- tion of nerve ends on the skin, which is felt by the test person as a sensation resembling as a knock or pinch.
• the sensation may also be slightly painful if the stimulated area coincides with a greater mass of muscles.
• the sensations felt on the scalp cannot be eliminated by any conventional technique known in the art.
• Magnetic stimulation by conventional techniques also includes a strong sonic bang that evokes an auditory sensation. This sound effect can be attenuated but not generally eliminated through the use of hearing protectors.
• Both the stimulation of the scalp and the sonic bang emitted by the stimulation coil activate the sensory nerve paths leading to the brain and, thus, the brain areas associated with sensory information.
• This brain activation interferes with the magnetic stimulation of the brain evoked directly by the stimulating electromagnetic field. Therefore, it is often difficult to identify whether a given result of stimulation is caused by direct stimulation of the brain or evoked by the sensory feelings on the scalp and the sonic bang heard by the test person.
• fake magnetic stimulation refers to stimulation that produces the same sensory and auditory stimulation as a real magnetic stimulation, yet inducing such a low field on the brain that cannot cause direct stimulation of nerve cells in the brain.
• Fake magnetic stimulation by means of conventional techniques and methods is accomplished by moving or rotating the coil into different positions above the head so that the field induced over certain areas of the brain is diminished.
• Another problem of conventional technique is that the change of coil position and, thus, the change of stimulation method is relatively easy to detect by the test person.
• the goal of the invention is achieved by producing the fake magnetic stimulation through the induction of at least two variable magnetic fields so that at least two of the magnetic fields are oriented in different directions, e.g., opposite to each other in the target area.
• the directions and magnitudes of the magnetic fields are set so as to attain partial cancellation of the electric fields, which are induced by the varying magnetic fields, within the target area such as the brain tissue, in a manner that avoids causing essential stimulation of the target area tissue by the direct effect of the fake stimulation field.
• the magnetic fields oriented in different directions can be produced using, e.g., two or a greater number of coils fed by varying currents. Alternatively, a suitable formed coil having, e.g., a figure-of-eight shape can be used.
• the exterior field must be so strong as to attain stimulation of the exterior tissue such as the scalp possibly overlying the target area.
• the magnetic field for the real deep-stimulating effect can be induced using the same coils mentioned above or, alternatively, at least one of them.
• the stimulation is attained by feeding the coils with such varying currents that cause the electric fields induced by the coils to sum in the target area such as the brain tissue simultaneously exciting both the nerve cells of the target area and the possibly overlying tissue layer such as the scalp and the muscles associated therewith.
• both the real and the fake magnetic stimulation pulses can be issued without physically moving the coil or plurality of coils.
• the current pulses fed to the coils during both the fake and the real magnetic stimulation are kept essentially equal in order to maintain the sound level of the sonic bang emitted by the coils essentially unchanged during both of these stimulation operations.
• the invention is also applicable to the stimulation of the peripheral nervous system, muscles and spinal cord. Instead of man, a test animal for instance may be the subject of stimulation.
• the response of the stimulating field on the actual target area such as the brain can be measured and assessed by subtracting the responses of the fake magnetic stimulation from those of the real magnetic stimulation.
• the method according to the invention is characterized by what is stated in the characterizing part of claim 1.
• the apparatus according to the invention is characterized by what is stated in the characterizing part of claim 9.
• the invention offers significant benefits.
• the test person has no possibility of detecting a change of the stimulation mode from a movement of the coil.
• the fake magnetic stimulation is achieved by moving the coil over another brain area, whereby a risk arises that the activation of a different brain area subjected to the fake magnetic pulse may affect the results of the test session.
• the present invention has the benefit of eliminating a direct effect of local stimulation on the brain and, instead, permits the direct stimulating effect of the fake magnetic pulse to be applied in a controlled and minimized manner.
• the invention can be applied using, e.g., electronic control of the stimulation current fed to the stimulator coils, whereby the operator of the stimulator can easily control the stimulator apparatus and select a desired mode of stimulation.
• the stimulation mode whether the real or the fake magnetic stimulation, may be selected manually, e.g., by pressing a key or automatically in a computer-aided environment.
• the invention may also be applied so that the stimulation mode is determined by an algorithm stored in a control computer or using a random sequence of selection, which allows an improved method of assessing the effect of magnetic stimulation applied as, e.g., a therapeutic treatment.
• Figure 1 shows the block diagram of an apparatus according to the invention suited for applying both real and fake magnetic stimulations
• Figure 2 shows the circuit diagram of pulsing circuit suitable for use in a stimulator apparatus according to the invention.
• the invention can be applied using two coils, for instance, whereby at least one of the coils is equipped with an electronic or manual selection facility of coil current polarity.
• the electromagnetic fields produced by the coils are summed over the target area and its immediate surroundings thus causing during brain stimulation, for instance, simultaneously both the activation of the brain cells and a sensation on the scalp.
• the coils are fed with currents running in the same direction, the fields cancel each other at least partially, whereby the field strength in the target area such as the brain falls to a low level insufficient for stimulating nerve cells.
• the near field induced by the coils in their vicinity such as on the scalp remains preferably sufficiently strong to stimulate, e.g., the scalp and the underlying muscles.
• the method according to the invention for producing a real magnetic stimulation effect and/or a fake magnetic stimulation effect in a biological tissue comprises the steps of:
• At least two electromagnetic fields are induced in a biological tissue for producing both the real magnetic stimulation and the fake magnetic simulation.
• the fields are induced so that their directions are oriented essentially codirectional in the target area in order to obtain a mutually augmenting effect thereof and, resultingly, to form an electromagnetic field capable of essentially exciting a biological tissue.
• the generation of the fake magnetic stimulation effect is accomplished through changing the direction of at least one of the induced electromagnetic fields opposite to the codirectional field employed for producing said real magnetic stimulation, whereby at least two electromagnetic fields will be superimposed essentially in opposite directions in the target area so as to cancel the effect of each other and to produce an electromagnetic field in the target area weak enough not to essentially excite the biological tissue such as the brain.
• both the real and the fake magnetic stim- ulation are produced using essentially a single apparatus setup and essentially equal coil pulsing power levels, whereby any possible side effects associated with the real and the fake magnetic stimulation such as sensations on the scalp and an auditory response caused by the noise emissions of the apparatus remain essentially unchanged when switching between the real and the fake magnetic stimulation modes.
• the apparatus shown in Fig. 1 comprises magnetic stimulator coils la, lb located in a parallel position close to the object being stimulated, a current source 4 feeding current to said coils la, lb, a switch device 3 serving to reverse the current to be fed by said current source 4 in the coil la, and current feed conductors 2a, 2b, 2c con- necting said current source 4 to said switch device 3 and to said coils la, lb.
• the switch device 3 has at least a first terminal and a second terminal for connection to the coil la, a third terminal for connection to the coil lb and a fourth terminal for connection to the current source.
• the apparatus may also include a control unit adapted to control the functions of the current source 4 and the switch device 3. For simplicity, the control unit is omitted from the diagram of Fig. 1.
• the conductors 2a, 2b, 2c are connected so that conductors 2a join the first and second terminals of the coil la to the first and second terminals of the switch device 3, the conductors 2b connect the first terminal of the coil lb to the current source 4 and the second terminal of the coil to the third terminal of the switch device 3, and the conductor 2c connects the fourth terminal of the switch device 3 to the current source 4. Then, the switching elements of the switch device 3 can connect the conductor 2b attached to the third terminal of the switch device 3 on the conductor 2a which is connected either on the first or second terminal and, respectively, the conductor 2c leaving the fourth terminal of the switch device 3 either on the conductor 2a connected to the second or first terminal.
• the coils la and lb are connected in series and the current pulse fed by the current source 4 can be passed via both coils la, lb so that the direction of the current via the coil la can be set by the switch device 3 to be either codirectional with or reverse to the current via the coil lb.
• the switch device 3 may have a design permitting a connection between the third and fourth terminals, too, whereby conductors 2b and 2c can be directly connected to each other. In this circuit connection, the coil la is bypassed and the current pulse fed by the current source 4 is passed via the coil lb only.
• a current pulse of 1-20 kA with a duration of 50-1000 ⁇ s is fed to the magnetic stimulator coils la, lb.
• the current pulse is formed by a pulsing circuit comprising coils la, lb, current conductors 2a, 2b, 2c, the switch device 3 and the current source 4.
• the current source 4 shown in Fig. 2 comprises a capacitor 5 connected in parallel with a power supply 6 and, connected in series with these, a thyristor switch 7 paralleled with a diode 8.
• the current pulse is typically formed by first charging the capacitor 5 to a voltage of 0.5 - 4 kV by the power supply 6 and then rapidly discharging the stored energy of the capacitor 5 into the coil lb or, alternatively, the coils la, lb via the conductors 2a, 2b, 2c.
• the discharge of the energy storage capacitor 5 is initiated by triggering the thyristor switch 7 conductive at a desired instant of time.
• the switch device 3 is set appropriately to selected the direction of current pulse to be passed via at least one of the coils, which in the illustrated circuit is coil la.
• a general function of the switch device is to connect at least one of the coils as a part of the pulsing circuit and to select the direction of the applied current pulse in at least one of the coils.
• a simple type of switch device 3 based on manually connectable connectors has a switch device construction 3 comprising a first and a second connector capable of accepting a first and a second mating connector attached to the ends of the conductors 2a of the coil la. Hence, the direction of current to be passed via the coil la can be set as desired by proper interconnection of the mating connectors.
• the switch device 3 can be implemented using, e.g., a construction with a first and a second two-position switch, a first and a second conductor wired to the first and second terminals of the coil plus a first and a second auxiliary conductor wired to said first and said second terminal of said coil.
• the switches, conductors and auxiliary conductors are arranged in the switch device 3 so that the first switch in its first position passes current to said first conductor of the coil and in its second position to said second auxiliary conductor, while the second switch in its first position passes current to said second conductor of the coil and in its second position to said first auxiliary conductor.
• the direction of the current pulse to be passed via the coil can be selected by proper setting of the switch positions.
• the switches When both switches are set in their first positions thus making the above-described connections to the respective conductors, the current is passed via the coil in a first direction and when the switches are set in their second position, that is, passing the current along the auxiliary conductors, the direction of the current pulse via the coil is reversed.
• the switches may be solid-state switch elements or mechanical switch components.
• the apparatus according to the invention may also be implemented by providing each of the coils la and lb with a separate pulsing circuit.
• one of the pulsing circuits may operate in the same manner as the pulsing circuit shown in Fig. 2.
• the other pulsing circuit can be modified from the circuit configuration of Fig. 2, e.g., by replacing the diode 8 with a thyristor switch.
• the charging polarity of the capacitor in the second pulsing circuit may be selected in a desired manner and, according to the selected charging polarity, either the first or the second thyristor switch is triggered conductive to pass the current pulse via the coil in a desired direction.
• One alternative arrangement for producing fake magnetic stimulation can be realized, e.g., using two magnetic stimulators each having a single stimulator coil.
• the coils are placed adjacent to each other on the test object.
• the fake stimulation is delivered by mechanically reorienting one of the coils by 180°, whereby the directions of the electromagnetic fields act opposite to each other.
• this technique of alternating between the fake and the real magnetic stimulation is extremely clumsy.
• Another alternative technique is to use one magnetic stimulator having a separate fake stimulator coil connected thereto during the administration of the fake stimulation.
• the fake stimulator coil has an external construction identical to that of the actual stimulator coil but, however, having an internal design capable of inducing the field pattern required for fake stimulation.
• a figure-of-eight coil can be used for producing the fake stimulation field, whereby the closed coil housing contains two coils, one of which being equipped with an optional selection of coil current direction.
• the coil currents are varied in proportion to each other during the test session from the values producing a real magnetic stimulation stepwise toward a fake stimulation and back.
• a benefit of this technique is that the field strength induced in the brain tissue, for instance, can be changed in a varying manner without causing an essential variation in the sensory or auditory sensation experienced by the test object.

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• 1998
  • 1998-07-10 FI FI981595A patent/FI105163B/fi not_active IP Right Cessation
• 1999
  • 1999-07-01 EP EP99934732A patent/EP1096973B1/de not_active Expired - Lifetime
  • 1999-07-01 WO PCT/FI1999/000587 patent/WO2000002624A1/en active IP Right Grant
  • 1999-07-01 DE DE69937640T patent/DE69937640T2/de not_active Expired - Lifetime
  • 1999-07-01 CA CA002336955A patent/CA2336955C/en not_active Expired - Fee Related
  • 1999-07-01 US US09/743,382 patent/US6537197B1/en not_active Expired - Lifetime
  • 1999-07-01 DK DK99934732T patent/DK1096973T3/da active

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